This invention relates to an apparatus for estimating frequency properties as in the preamble of claim 1. Furthermore, the invention relates to an apparatus for estimating the spectrum of a signal as in the preamble of claim 7. The invention further relates to a signal recognition system, a data compression system and a signal improvement system device including such apparatuses and methods for performing functions of the apparatus.
Apparatuses as described above, are known from the article xe2x80x9cUsing an Auditory Model and Leaky Autocorrelators to Tune In to Speechxe2x80x9d by T. Andringa, published in ESCA Eurospeech 97, Rhodes, Greece, ISSN 1018-4074, pp. 2859-2862. From this Andringa 1997 article, it is known to make use of an auditory model which imitates the working principles of the basilar membrane. The output of the segments of the model is used as an input for a set of leaky autocorrelator units which are tuned to a particular, fixed, periodicity. The activity of the responsive autocorrelator units as a function of the segment number is then a direct measure for the spectrum of the periodic signal to be detected.
With the apparatus described in this prior art document, it is possible to reconstruct an energy spectrum of a signal whose fundamental period is both known and constant. However, a problem presents itself in that the known device does not provide for the correct and or optimal reconstruction of the energy spectrum when the period is unknown, is not constant, or both. The object of the invention is to provide a device which enables a correct reconstruction of the signal when the period of the sound signal is unknown and/or is not constant.
In a first aspect of the invention to that end the invention provides a device as claimed in claim 1. In a second aspect of the invention to that end the invention provides a device as claimed in claim 8.